1. Field of the Invention
The present invention relates to a water-removing material usable for hydrophobic liquids consisting of a fiber assemblage containing water-swellable fibers. At least a part of the fiber outer layer is composed of a hydrophilic, cross-linked polymer (hereinafter referred to as hydrogel) and the remainder is composed of an acrylonitrile polymer (hereinafter referred to as AN polymer) and/or another polymer. The invention also relates to a water-removing filter formed into the shape of a tube by winding said fiber assemblage around an internal tubular support, or by compressing said fiber assemblage into the shape of a tube.
2. Description of the Prior Art
In recent years, polymers having a high degree of water-swellability and water-insolubility (hydrogels) have been used in a wide field of applications because of their particular functions. For example, attempts have been made on applications to diapers, sanitary products, etc. by utilizing the instantaneous high water-absorbing power of these polymers; applications to soil-improving materials, instant sandbags, etc. by utilizing their high water-retentive capacity; or applications to soft contact lenses, artificial internal organs, surgical seaming materials, etc. on account of their intimate affinity to human tissues, and among these applications some are already entering a practical stage.
On the other hand, there is a strong demand for removing water contained in hydrophobic liquids such as organic solvents, lubricating oils, etc. to reuse such liquids or to prolong their useful life. For this purpose, granular products of inorganic salts such as silica gel, zeolite, etc. are used in some cases. Although it is possible to remove water to some extent by such inorganic salts, their water removing power is extremely low. In addition, such salts involve an intrinsic defect of remaining in the liquids after purification in slight quantities, and therefore their fields of use had to be limited. Also, the use of fibers produced from natural pulp, etc. having some degree of moisture- or water-absorbing properties is attempted in some cases, but their water-removing ability is extremely low and they are lacking in practical usability.
In such a situation, we paid attention to the instantaneous high water-absorbing power of said water-swellable polymers (hydrogels), and attempted to determine if it is possible to utilize them as a water-removing material for the above-mentioned hydrophobic liquids. However, in the case of using a hydrogel in the form of granules, they absorbed water and swelled instantaneously due to their excellent water-absorbing power, and clogged the interspaces or gaps among the granules. Therefore, we had to stop the water-removing treatment after a very short time. To avoid such gap clogging, we tried to use a hydrogel in fiber form, and found that it was possible to prolong the time of the water-removing treatment to some degree in comparison with granular hydrogels. But, by reason of swelling and deterioration of the fibers, we were not able to solve the problem of gap clogging and therefore it was impossible to cause such a fiber form hydrogel to exhibit its water-absorbing power.